Solid support-based chromatographic methods have been extensively applied in separation science for many years. Harris, Quantitative Chemical Analysis, 2nd ed., W. H. Freeman and Co., New York (1987); Skoog, Principles of Instrumental Analysis, 3rd ed., Saunders College Publishing, New York (1985); Giddings, Unified Separation Science, John Wiley & Sons, New York, (1991)! Excellent chemical separations can be achieved due to the inherent variables of solid/liquid chromatography Skoog, Principles of Instrumental Analysis, 3rd, ed., Saunders College Publishing, New York (1985)! that include the ability to vary both the support material and mobile phase. Several advantages over solvent extraction include the immobilization of the extractant and the absence (or decreased need in the case of extraction chromatography) of organic solvent diluents. As for solvent extraction, scale-up of solid support-based chromatographic methods is feasible with the major concern of the pressure drop across a large column balanced by the simplicity of the chromatographic apparatus versus liquid/liquid contactor apparatus.
Due to the rich history of liquid/liquid aqueous biphasic separations for biological separations, Poly(Ethylene Glycol) Chemistry: Biotechnical and Biomedical Applications; Harris, ed., Plenum Press, New York (1992); Aqueous Two-Phase Systems, Walter and Johansson, eds., in Methods in Enzymology, Academic Press, San Diego, Vol. 228 (1994); Albertsson, Partition of Cell Particles and Macromolecules, 3rd ed., John Wiley & Sons, New York (1986); Partitioning in Aqueous Two-Phase Systems. Theory, Methods, Uses and Applications to Biotechnology, Walter, Brooks and Fisher, eds., Academic Press, Orlando (1991)! work on solid-supported biphasic separations has focused on biological species. No work has been reported in the area of aqueous biphasic partitioning of metal ions using solid support separation particles.
The chelation properties of solid-supported short chain polyethers have been investigated, but the mobile phases were largely aqueous acids and the systems lacked genuine aqueous biphasic behavior. The chelation properties of the high molecular weight poly(ethylene glycols) (PEGs) is generally perceived to be quite low. Consequently, high molecular weight PEG resins have not been investigated for ion separations.
The major variables influencing liquid/liquid aqueous biphasic separations, type and concentration of polymer and salt and polymer molecular weight, are important variables to consider in the design of aqueous biphasic chromatographic materials. The current focus is on chaotropic metal ion separations from solutions of high ionic strength because most metal-containing waste streams have relatively high concentrations of matrix ions.
Two major drawbacks to aqueous biphasic separations operating in the liquid/liquid mode are loss of the phase-forming components, PEG or salt, due to their high solubilities in water and the difficulty in stripping partitioned solutes. Because high concentrations of the phase-forming components are required to sustain a two-phase system, any loss of PEG or salt is of concern. In addition, different concentrations of phase-forming components have been shown to affect metal ion distribution ratios in liquid/liquid systems. Rogers et al., Solvent Extr. Ion Exch., (in press 1995); Rogers et al., Aqueous Biphasic Separations: Biomolecules to Metal Ions, (in press 1995)!
More importantly, once the solute of interest has been partitioned to the upper PEG-rich phase of an aqueous liquid/liquid biphase, its isolation from this matrix has proven to be difficult. The back extraction conditions vary from chemical destruction of the extractant and partitioned complex to chemical reduction of the partitioned species pertechnetate reduction by tin(II) chloride!. Rogers et al., Solvent Extr. Ion Exch., (in press 1995); Rogers et al., Aqueous Biphasic Separations: Biomolecules to Metal Ions, (in press 1995)!
Examination of the salts that induce aqueous liquid/liquid biphase formation of PEG solutions by the present inventors has indicated that those salts are among the materials referred to in the art as lyotropes or lyotropic agents. Such salts tend to structure water, and the structure provided to the water by a lyotropic salt is thought to cause salting out of the PEG phase.
Polyethylene glycols have been bound to a variety of different materials, with the choice of support based primarily on the desired application. Solid-supported short chain PEGs have been grafted to styrene-based resins for use as phase transfer catalysts in organic synthesis, Regen et al., J. Am. Chem. Soc., 101:116 (1979); Yanagida et al., J. Org. Chem., 44:1099 (1979); Fukunishi et al., J. Org. Chem., 46:1218 (1981); Heffernan et al., J. Chem. Soc., Perkin Trans. 2:514 (1981); Kimura et al., Synth. Commun., 13:443 (1983); Kimura et al., J. Org. Chem., 48:195 (1983)! and to urethane foams to act as potential metal ion chelators. Jones et al., Anal. Chim. Acta, 182:61 (1986); Fong et al., Talanta, 39:825 (1992)! Polyethers have also been bound to various surfaces to decrease protein adhesion in biomedical applications Nagaoka et al., Antithrhombogenic Biomedical Material, Toray Industries, Inc. (1983); Toyobo Co., Antithrhombogenic Membranes, Toyobo Co. (1983)! and medium weight PEGs have been fused to silica capillaries for a variety of separations. Nashabeh et al., J. Chromatogr., 559:367 (1991); Herren et al., J. Coll. Interf. Sci., 115:46 (1987)! High molecular weight PEGs have been bound to silica Matsumoto et al., J. Chromatoqr., 187:351 (1980)! and Sepharose Matsumoto et al., J. Chromatogr., 187:351 (1980); Matsumoto et al., J. Chromatoqr., 268:375 (1981); Matsumoto et al., J. Chromatoqr., 285:69 (1984)! primarily for polymer/polymer separations of biomolecules. Two recent reviews of PEG chemistry also point to the utility of solid-supported PEGs for bioanalytical separations. Poly(Ethylene Glycol) Chemistry: Biotechnical and Biomedical Applications, Harris ed., Plenum Press, New York (1992); Aaueous Two-Phase Systems, Walter et al., eds., in Methods in Enzymology Academic Press, San Diego, 228 (1994)! Each of the previously mentioned materials served as chelators or hydrophilic coatings to promote or inhibit different types of adsorption processes.
The importance of .sup.99m Tc in nuclear medicine and the problems associated with disposal of .sup.99 Tc in nuclear waste require new and better separations technologies for this element. In radiopharmacy, the short-lived .sup.99m Tc (t.sub.1/2 =6 hours) that decays to .sup.99 Tc (t.sub.1/2 =2.12.times.10.sup.5 years), is used in the vast majority of all medical procedures utilizing radioisotopes. Boyd, Radiochim. Acta, 30:123 (1982); Steigman, The Chemistry of Technetium in Medicine, National Academy Press, Washington, D.C. (1992)!
One of the more common ways to access .sup.99m Tc is by eluting the pertechnetate ion (TcO.sub.4.sup.-1), a chaotropic anion, from an alumina column containing .sup.99 MoO.sub.4.sup.-2 ion (t.sub.1/2 =66.7 hours), itself obtained by neutron activation irradiation of .sup.98 Mo or as a .sup.235 U fission product. So-called "instant technetium" involves the solvent extraction of .sup.99m TcO.sub.4.sup.-1 from an alkaline solution of Na.sub.2.sup.99 MoO.sub.4 using methyl ethyl ketone. Both methods suffer disadvantages including the presence of organic impurities and low radiochemical yield. Boyd, Radiochim. Acta, 30:123 (1982); Steigman, The Chemistry of Technetium in Medicine, National Academy Press, Washington, D.C. (1992); Lamson et al., J. Nucl. Med., 16:639 (1975); Nair et al., Radiochim. Acta, 57:29 (1992)!
Relatively high levels of .sup.99 TcO.sub.4.sup.-1 are present in the highly alkaline waste storage tanks at Westinghouse Hanford Fong et al., Talanta, 39:825 (1992)! and Savannah River Walker et al., Mat. Res. Soc. Syms. Proc., 44:805 (1985)!, among others. Technetium-99 is a fission product in nuclear fuel burn-up. Its long half life and its environmental mobility (as TcO.sub.4.sup.-1) present long term storage problems. Mobius, et al., "Gmelin Handbook of Inorganic Chemistry, Tc, Technetium: Metal Alloys, Compounds, Chemistry in Solution", 8th ed., Supplemental vol. 2, p. 243, Kugler & Kellar, eds., Springer-Verlag, Berlin (1983); Jones, "Comprehensive Coordination Chemistry", Vol. 6, p. 881, Wilkinson et al., eds., Pergamon Press, Oxford (1987)!
Current extraction technologies for Tc run the gamut from solvent extraction to ion exchange in batch and chromatographic separations, and precipitation reactions. Mobius, et al., "Gmelin Handbook of Inorganic Chemistry, Tc, Technetium: Metal Alloys, Compounds, Chemistry in Solution", 8th ed., Supplemental vol. 2, p. 243, Kugler & Kellar, eds., Springer-Verlag, Berlin (1983)! The synthetic organic reagents or resins used are often subject to radiation damage (in high level nuclear waste applications) and large cations (e.g., UO.sub.2.sup.+2, Zr.sup.+4) can be coextracted. Mobius, et al., "Gmelin Handbook of Inorganic Chemistry, Tc, Technetium: Metal Alloys, Compounds, Chemistry in Solution", 8th ed., Supplemental vol. 2, p. 243, Kugler & Kellar, eds., Springer-Verlag, Berlin (1983); Jassim et al., Solvent Extr. Ion Exch., 2:405 (1984); Kolarik et al., Solvent Extr. Ion Exch., 7:625 (1989)! New separations techniques and tailored waste forms are needed for selective removal and immobilization of .sup.99 Tc.
The pertechnetate ion partitions to the polymer-rich phase in liquid/liquid PEG-based aqueous biphasic systems from a variety of salt solutions including OH.sup.-1, CO.sub.3.sup.-2, SO.sub.4.sup.-2 and PO.sub.4.sup.-3. Increasing the incompatibility between the two phases forces more of the TcO.sub.4.sup.-1 into the PEG-rich phase. This can be accomplished either by increasing the salt concentration or increasing the PEG-2000 concentration from about 20 weight percent to about 70 weight percent of the aqueous solution.
Tungsten (W) and rhenium (Re) are in the same groups in the periodic Table as are molybdenum and technetium, respectively, and share many chemical reactivities with their fellow group members. The perrhenate anion (ReO.sub.4.sup.-1), particularly as .sup.188 ReO.sub.4.sup.-1 (t.sub.1/2 =16.9 hours) and .sup.186 ReO.sub.4.sup.-1 (t.sub.1/2 =90 hrs) are finding increasing use of therapeutic radiopharmaceuticals as a bone cancer pain palliative and when linked to monoclonal antibodies. As .sup.99 TcO.sub.4.sup.-1 is formed from .sup.99 MoO.sub.4.sup.-2, .sup.188 ReO.sub.4.sup.-1 is formed from .sup.188 WO.sub.4.sup.-2. Several systems for separating .sup.188 ReO.sub.4.sup.-1 anions from solutions containing .sup.188 Wo.sub.4.sup.-1 anions similar to those used for separating .sup.99 TcO.sub.4.sup.-1 anions from .sup.99 MoO.sub.4.sup.-2 anions have been reported. Lisie et al., J. Nuc. Med., 32:945(1991); Schaad et al., J. Nuc. Med., 32:1090(1991); Ehrhardt et al., J. Nuc. Med., 34:38P (1993)!
In addition to technetium and rhenium, several other chaotropic metal anions are of particular interest for separation and recovery. For example, effluents containing silver, cadmium, mercury, arsenic, selenium, chromium, lead and barium are regulated. The Y-12 site at Oak Ridge is reported to have mercury contamination problems. In addition, Hg-197 as .sup.197 HgCl.sub.2 is used in kidney scans. Choppin et al., Radiochemistry and Nuclear Chemistry, 2nd ed., Chapter 9, Butterworth-Heinemann Ltd., Oxford (1995) pages 266-276! Precious metals such as gold and silver present in mine tailings also require enhanced recovery processes. Elimination of metal ions from waste streams via complexation of silver, gold, cadmium, mercury and lead with halide or pseudohalide anions is desirous.
Radioactive iodide anion, particularly as I-123, I-125 and I-131, are widely used in radiopharmacy. These anions are mostly used for thyroid studies, but are also useful for kidney studies. Ehmann and Vance, Radiochemistry and Nuclear Methods of Analysis, Chapter 10, Wiley, New York (1981) pages 331-342; Friedlander et al., Nuclear and Radiochemistry, Chapter 11, Wiley, New York (1981) pages 442-448!
In addition, I-129 is a fission product that is present in the waste tanks of the Westinghouse Hanford facility. Because of its long half-life (about 1.7.times.10.sup.7 years) and environmental mobilit, this nuclide needs to be removed from wastes. Chemical Pretreatment of Nuclear Waste for Disposal, Swanson et al. eds., Plenum, New York 1994) pages 155-209!
It would therefore be beneficial if the selective binding of chaotropic anions to PEG resins found in aqueous biphasic separations could be adapted to a solid support-based separation and recovery process, while at the same time, overcoming the problems inherent in recovering the chaotropes from an aqueous biphasic separation system using a solid phase that is not adversely affected by radiation present. The discussion that follows provides one solution to the chaotrope recovery problem for many of the above-named elements, as well as others.